In multiple user systems, that is, systems wherein the word processing system is utilized by several different individuals performing the same or different operations, it is desirable to have flexibility in the systems configuration and the utilization of the computing capability provided. The systems are desirably such that they can be modified to add on additional capability and functions or to subtract capability and functions so that the systems can be configured conveniently to achieve a particular objective. In general, systems have been developed incorporating dual (or a greater number) of displays. Some of these systems have plural display with each display exhibiting identical information, such as in the case of plural CRT monitors coupled to a common signal source.
Examples of various configurations that users may desire involve the number of printers that a system incorporates, the number of data entry stations that the system incorporates, and the manner in which the system shares the resources available for performing various functions. Word processing systems have been developed employing distributed processing. One word processing system employs microcomputers to implement distributed intelligence in multiple station systems.
The previous systems that have been configured for multiple user application have been limited in the flexibility that they provide in terms of systems configuration modification and capability. One example of a multiple user system involves a single central processing unit to which various subsystems are attached. One such example is shown in U.S. Pat. No. 3,654,609 granted to Bluethman et al. This reference discloses an editing system including a CRT display which displays input characters in a proportionally spaced representation. The text character representations are stored in memory and are accessed by a processor. In this system, additional subsystems are attached to operate in conjunction with the single central processing unit. As additional subsystems are attached to the configuration to support additional users, the single processor begins to reach the limit of its capability. The response time for the central processor unit to respond to subsystem requests for data manipulation soon exceeds the time constraints for the additional subsystems. Moreover, should the single central processing unit fail, all of the subsystems are rendered inoperable and the entire system can not be utilized.
The invention disclosed in this cited reference requires the use of a large memory with the single central processing unit. The single central processing unit itself is more expensive and more critical to the operation of the entire system than components used in distributed configurations.
Another approach to the multiple user and subsystem word processing systems involves the dedication of subsystems to each particular function or task. An example of such an approach is shown in U.S. Pat. No. 3,815,104 granted to Goldman. In this system, the subsystems are hard wired and are each dedicated to a particular task. FIG. 1 in this reference, for example, clearly indicates that hardware is associated with each the function such as pagination, justification, clean up hyphen and keyboard interface. Thus, flexibility is very much constrained in terms of the hardware of the system.
The subsystems are connected to each other by means of a communications bus which includes a data bus, a special control and indicator bus, an address bus and a timing bus. Although the system utilizes distributed processing, each subsystem is rigid in that its function is designed into the hardware and it is not capable of being utilized for any other function.